Conversion of hydrocarbon oils



Feb. 3, 1942. C, H ANGELL 2,271,610

CONVERSION OF HYDROCARBON OILS Filed Aug. 3l, 1938 fanaenser 3 Patented Feb. 3, 1942 CONVERSION OF HYDROCARBON OILS Charles H. Angell, Chicago, Ill., assigner to Universal Oil Products Company, Chicago, Ill., a

corporation of Delaware Application August 31, 1938, Serial No. 227,816

(ci. 19e-s) 8 Claims.

The invention particularly refers to an improved process for the pyrolytic conversion of hydrocarbon oils (particularly light distillates such as gasoline or gasoline fractions of inferior antiknock value, naphtha or the like) into high yields of gasoline of good antiknock value, and preferably of controlled vapor pressure, with the simultaneous production and separate recovery of a normally gaseous product containing a high concentration of relatively heavy gases such as l separated into vaporous and non-vaporous cor'nponents, the vapors fractionated to form reflux condensate, the resulting fractionated vapors, which consist essentially of gases and materials boiling within the range of the desired. gasoline product, subjected to condensation, the resulting distillate separated from remaining uncondensed and undissolved gases, the distillate stabilized to reduce its vapor pressure to the desired degree by liberating therefrom regulated quantities ofthe dissolved gases, said uncondensed and undissolved gases intimately contacted withan absorber oil comprising regulated quantities of the reflux condensate formed by said fractionation, whereby to separate desirable heavy components by absorption from lighter components of said gases, substantially stripping the resulting enriched absorber oil of dissolved gases, recovering materials thus liberated from the enriched absorber oil and liberated from said distillate by said stabilization thereof as a normally gaseous product rich in readily polymerizable ol-ens, such as propane and/or butenes, and commingling regulated quantities of the resultant strippedabsorber oil with the heated products of said cracking operation,

whereby to accomplish at least a portion of the aforementioned cooling of said products.

The invention specifically contemplates the use of other suitable oil, either from within the system or from an external source, as an absorbent for the desired heavy gases, either in conjunction with the use of, or instead of reflux condensate. The use of other or additional material as absorber oil is particularly desirable in cracking operations of the type wherein only relatively small quantities of reux condensate are produced. However, even in such operations a cycle of reflux condensate will eventually be built up within the system, when it is utilized as absorber oil and the stripped absorber oil is commlngleci with the heated conversion products. Therefore, the use of additional absorber oil will only be a necessity in starting the operation.

In addition to the strippedfabsorber oil, other suitable oil from withinthe system or from an external source may be utilized for effecting the desired cooling of the hot conversion products by directly commngling the same therewith. It is also within the scope of the invention to effect a portion of this cooling by indirect heat exchange between the heated products and any suitable cooling material and/ or by reducing the pressure between the heating step and the vapor separating step of the system. Any or all of these methods of cooling may be employed in conjunction with the use of stripped absorber oil in the manner above described.

Although the specific embodiment of the invention, above described, illustrates its adaptability to reforming operations, the feature of the invention relating to the use of reflux condensate, or other substantially gas-free condensate from within the system, as absorber oil and the feature relating to the use of stripped absorber oil as a cooling medium for relatively hot conversion products of the process are not limited to use in a reforming system, since either or both of these l features may be employed to advantage in practically any type of cracking operation. Also.' the stripped absorber oil may, within the scope of the invention, be utilized for cooling or quenching of the hot conversion products at any point in the system wherein such cooling or quenching is advantageous.

The accompanying diagrammatic drawing illustrates one specific form of apparatus embodying the features of the invention, as applied to a system for reforming light distillate. This drawing and the following description thereof will f serve to adequately illustrate the features of the invention, but is not to be construed as a limitation for the reasons above mentioned.

Referring to the drawing, the distillate charging stock is supplied through line l and valve 2 to pump 3 by means ofwhich it is fed through line 4 and valve 5 to heating coil Gand is then heated to the desired cracking temperature, preferably at a substantially superatmospheric pressure, by means of heat supplied from a furnace 1. The charging stock may, of course, be preheated to below cracking temperature in any well known manner, not illustrated, prior to its introduction into coil 6 and although coil 6 and furnace 1 are illustrated in a diagrammatic manner, they preferably comprise one of the well known forms of cracking heater, wherein the light distillate undergoing treatment is heated to an active cracking temperature and then maintained for a predetermined time at a relatively high active cracking temperature.

Highly heated conversion products are discharged from coil 6 through line 8 and, after being cooled sufficiently to preclude their excessive continued conversion, are introduced into separating chamber I0. This cooling is accomplished, at least in part, by directly commingling substantially stripped absorber oil from a subsequent step in the system with the heated products passing through coil 8, in the manner which will be later described. A portion of the desired cooling is preferably also accomplished by substantially reducing the pressure imposed upon the stream of heated products as they pass through valve 9 in line 8, thus liberating latent heat and substantially reducing the pressure employed in chamber I as compared with that employed at the outlet of coil 6.

Separation of vaporous and residual liquid products is accomplished in chamber I0 and, preferably, to assist cooling in this zone, a suitable cooling and refluxing oil is supplied to the upper portion of the chamber, as will be later described. The liquid residue which remains unvaporized in chamber I0 is removed from the lower portion of this zone through line II and valve I2 to cooling and storage or elsewhere, as desired, and the vaporous products are directed from the upper portion of chamber I0 through line I3 and valve I4 to fractionation in fractionator I5.

Substantially all of the components of the vapors supplied to fractionator I5, which boil above the range of the desired gasoline product, are condensed as reflux condensate in this zone. Substantially all or a portion of the high-boiling fractions of the reflux condensate so produced are directed from the lower portion of fractionator I5 through line I 6 and valve I1 to pump I8 wherefrom they may be discharged, all or in part, from the 'system through line I9 and valve 20 or regulated quantities of this material may be directed by means of line 2I and valve 22 into the upper portionof chamber I0 to serve as a cooling and reiiuxng medium in this zone. The invention also specifically contemplates the use of'reflux condensate removed from the lower portion of fractionator I5 as an absorbent for desired highboiling components of the gases `produced within the system. Provisions for thus utilizing the reflux condensate are illustrated.`and will be later described. It is also within th scope of the invention to return reflux condensate so produced in fractionator I5 to heating :coil 6 for further cracking. although well kno means for accomplishing this are not illustrated in the drawing.

When desired, selected low-boiling fractions of the reflux condensate formed in fractionator I5. which may either consist essentially of materials boiling above the range of the desired final gasoline product or may comprise relatively heavy able intermediate point in fractionator I5 through gasoline fractions, may be directed from a suitline 23 and valve 24 to reboiling and stripping column 25, wherein this material preferably is substantially stripped of dissolved gases and any other undesired low-boiling fractions by passing a suitable heating medium through closed coil 26 in the lower portion of column 25 in indirect heat exchange with the light 'reflux condensate collected therein. The vapors and/or gases evolved in column are returned therefrom through line 21 and valve 28 to fractionator I5.

The reboiled and substantially stripped reflux condensate is directed from the lower portion of column 25 through line 29 and valve 30 to pump 3| wherefrom it is directed, as will be later described, to the absorption step of the system for use therein as an absorbent for desired highboiling components of the process gases.

Fractionated vapors and gases of the desired -end-boiling point are directed from the upper portion of fractionator I5 through line 32 and valve 33 to cooling and condensation in condenser 34, wherefrom the resulting distillate and uncondensed gases are supplied through line 35 and valve 36 to collection and separation in receiver 31. Gases which remain'uncondensed and undissolved in the distillate collected in receiver 31 may be released from the receiver and from the system through line 38 and valve 39. Preferably, however, a regulated portion or all of these gases are directed from receiver 31 through line 40 and valve 4I and through line 42 to absorber 43, wherein desired high-boiling components are recovered therefrom, as will be later described.

The distillate collected in receiver 31 may be removed therefrom, all or in part, through line 44 and valve 44 to storage or elsewhere, as desired. Preferably, however, this distillate, since it will normally contain substantial quantities of dissolved heavy gases in excess of those required to give it the desired vapor pressure, is subjected to stabilization to liberate the excess gases and reduce its vapor pressure to the desired degree. Provision is therefore made for supplying the distillate from receiver 31 through line 45 and valve 46 to pump 41 by means of which it is directed through line 48, valve 49, heat exchanger 50. line 5I and valve 52 to stabilizer 53.

The function of heat exchanger 50 is to impart to the distillate the heat required for its stabilization and, in the particular case here illustrated, another portion of the heat required is.

supplied to the unvaporized distillate which collects in the lower portion of stabilizer 53 by reboiling of the latter. This is accomplished by passing the distillate from the lower portion of the stabilizer through line 54 and valve 55 tov reboiler 56 wherein heat forreboiling is imparted thereto, as will be later described, by its indirect heat exchange with a suitable heating medium, and wherefrom the evolved vapors and gases are returned through line 51 to the stabilizing column. The reboiled and stabilized distillate is directed from reboiler 56 through line 51 and valve 58 to heat exchanger 50, wherein it serves as a heating `medium for the distillate being supplied to stabilizer 53 and is thereby partially cooled. The stabilized distillate is directed from heat exchanger 59 through line 59 and valve 60 to further cooling and storage or elsewhere, as desired. f Reboiling of the distillate undergoing'stabilization may, of course, be accomplished within the lower portion of the stabilizer, by well known means not illustrated, instead of in an external reboiler, when desired. In order to further control stabilization in stabilizer 53, a closed coil 6I is provided in the upper portion of this zone through which a suitable cooling mediumis passed, but any other well known means may be employed within the scope of the invention for cooling and controlling refiuxing within stabilizer 53. One such alternative means will be later described, although it is not illustrated in the drawing. s

The gases liberated from the distillate by stabilization in column 53 are removed from the upper portion of this zone through line 62 and may be directed, when desired, through valve 63 in this line and through line 42 to absorber 43 or they may be directed, all or in part, from line 62 through line 84, valve 65 and line 66 to condenser 61, wherein they are substantially condensed by indirect heat exchange with a suitable cooling medium passed through this zone and Wherefrom the resulting normally gaseous condensate and any uncondensed relatively light gases are directed through line 68 and valve 69 to collection and separation in receiver 18. The relatively light uncondensed gases may be released from receiver 10 and from the system through line 1I and valve 12 or they may be directed by means of line 13, valve 14 and line v42 to absorber 43. The normally gaseous condensate collected in receiver 10 will be a product rich in readily polymerizable olefins such as propene and/or butenes and is removed from the system to storage or directed to a polymerization system or elsewhere, as desired, through line 15 and valve 16. When desired, regulated quantities of the normally gaseous condensate collected in receiver 10 may be supplied by well known means, not shown in the drawing, to the upper portion of stabilizer 53 to directly commingle in this zone with the light fractions liberated from the stabilized distillate therein and serve as a cooling and refluxing medium.

The invention also contemplates the return of regulated quantities of the distillate collected in receiver 31 to the upper portion of fractionator I5 by well known means, not illustrated, wherein it serves as a cooling and reuxing medium by directly commingling therein with the vapors and gases undergoing fractionation in this zone'.

The gases supplied to absorber 43, as previously described, from receiver 31 and/or from stabilizer 53, as well as, when desired, from receiver 18 are intimately contacted in this zone with an oil capable of absorbing desirable high-boiling components of these gases such as propane and/or butanes and the corresponding olelins. Oil from an external source may be supplied through line 11 and valve I8 to the upper portion of absorber 43 for the purpose mentioned or, preferably, a suitable oil from within the system is utilized for this purpose, either alone or in conjunction u'ith absorber oil from an external source. To accomplish the latter mode of operation, provision is made, in the particular case here illustrated, for directing condensate from the lower portion of fractionator I5 from pump I8 through line 19, valve 88, line 8|, coil 82, line 83, valve 84, reboiler 56, line 85, valve 88, cooler 81, line 88 and valve 89 to the upper portion of absorber 43. Provision is also `made for directing light reflux condensate collected in reboiling and stripping column 25 from pump 3I through line 98, valve 9I, line BI, coil 82, line 83, valve 84, reboiler 56, line 85, valve 86, cooler 81, line 88 and valve 89 to the upper portion of absorber 43. By passing the absorber oil through coll 82, reboiler 56 and cooler 81 it is cooled sufficiently to function as an efficient absorbent for the desired high-boiling gases in absorber 83 and, in cooling, serves as a heating medium in coil 82, as will be later described, and in reboiler 56 for reboiling the distillate undergoing stabilization. These particular heat exchange steps are not an essential feature 'of the inventionA and may be omitted or replaced by other heat exchange steps,

when desired. Cooling of the absorbed oil toA the desired final temperature is accomplished in cooler 81 by passing the same through this zone in indirect heat exchange with any suitable cooling medium.

The relatively light gases, which remain unabsorbed in absorber 43, are released from the upper portion vof this zone and from the system to storage or elsewhere, as desired, through line 92 and valve 93.

In order to recover the desired heavy gases absorbed in absorption column 43, the enriched absorber oil from this zone is preferably heated and substantially stripped ol dissolved gases. This is accomplished, in the case here illustrated, by directing the enriched absorber oil from the lower portion of column 43 through line 94 and valve 95 to and through heat exchanger 96, wherein heat is imparted thereto, as will be later described, and thence through line 91 and valve 98 into stripping column 99. Reboiling of the absorber oil to substantially strip the same of disolved gases is accomplished, in the case here illt'istrated, by passing relatively hot reflux condensate from fractionator I5 through closed coil 82 in the lower portion of the stripping column.

However, any other suitable means of accomplishing this may be employed withim the scope of the invention. A closed coil |88, through which a suitable cooling medium is passed, is provided in the upper portion of stripper 99 to assist in separating evolved gases and normally liquid fractions in this zone. The gases evolved in stripper 99 are removed from the upper portion of this zone through line I8I and may be directed through valve |02 in this line and through line 66 to condenser 61, wherefrom the resulting normally gaseous condensate and uncondensed light gases are supplied, in the manner previously described, to receiver 10 or they may be supplied, preferably by way of condenser 34, to receiver 31, line |03 and valve |04 being provided, in the case here illustrated, for this purpose. Since receiver 31 is preferably operated at a somewhat higher pressure than that employed in absorber 43, in order to avoid the use of a compressor for supplying gases from the receiver to the absorber. a suitable pump, not illustrated, is preferably provided for supplying the enriched absorber oil from absorber 43 to stripper 99, when gases from the latter zone are returned to receiver 31. in

which case, stripping column 99 is operated at a somewhat higher pressure than receiver 31.

Absorber 43 is preferably so operated that at least a major portion of the gases recovered in the enriched absorber oil are relatively heavy gases such as propane and/or butanes and the corresponding olefins. Therefore, the same will apply to the gases released from the enriched absorber oil in stripper 99, and when these gases are returned to receiverv 31 they will increase the proportional amount of relatively heavy normally gaseous fractions in the materials supplied to this zone from fractionator I5, thus increasing the concentration of relatively heavy gases in the unstabilized distillate and decreasing the concentration of relatively light gases in the unstabilized distillate. Therefore, the gases removed from the upper portion of the stabilizer will contain a larger amount of the desired relatively heavy gases and a proportionally smaller quantity of the undesired light gases. 'Ihis simplies condensation in condenser 61 and improves the quality of the normally gaseous condensate recovered in receiver 10. When gases from stripper 99 are returned to receiver 31, gases from stabilizer 53 are suppliedto condenser 61 rather than `to absorber 43.

The substantially stripped absorber oil is removed from the lower portion of stripper 99 and directed, in the case here illustrated, through line |05 and valve |06 to and through heat exchanger 96, wherein it supplies to the enriched absorber oil a substantial quantity of the heat required for stripping the latter and wherefrom it is thence directed through line |01 and, when desired, may

be removed in part from the system to further cooling and storage or elsewhere, as desired, through line |08 and valve |09 or it may be supplied by pump and suitable lines, not illustrated, communicating with line |08 and coil 6, to the latter zone for further cracking. However, at least a regulated portion of the stripped absorber oil is preferably directed through valve |09 in line |01 to pump |I0 by means of which it is introduced through line into line 8 to commingle therein with the heated products passing from coil 6 to chamber |0, provision being made, in the case here illustrated, for supplying the stripped absorber oil to line 8 on either or both sides of pressure reducing valve`8 by means of lines ||2 and ||4 controlled by the respective valves ||3 and ||5. It is also within the scope of the invention, although means forV accomplishing this are not illustrated, to introduce all or a portion of the stripped absorber oil utilized as a cooling medium in line 8 directly into valve 9. Regulated quantities of the stripped'absorber oil may also be employed as a cooling medium within fractionator I5 or at any desired preceding point in the system by supplying the same thereto, by well known means not illustrated, and, when desired, the stripped absorber oil utilized as a cooling medium may be further cooled, following its discharge from the heat exchanger .96, by any well known means, not illustrated.

Also stripped absorber oil may by-.pass the heat exchanger 96 by well known means, not illustrated, in which case, any other suitable means may be employed for supplying heat to the enriched absorber oil passing from absorber 43 to stripper 99 or all the heat required for stripping m'ay be supplied to the bottoms collected in stripper 9|; Y

The preferred range of operating conditions which may be employed, in an apparatus such as illustrated and above described, to accomplish the desired results may be substantially as follows: The temperature employed at the outlet of coil 6 may range from 900 to 1050 F., or more, preferably with a superatmospheric pressure at this point in the system of from 200 to 1000 pounds, or thereabouts, per square inch. The heated products from coil 6 are preferably cooled to a temperature ofthe order of 750 to.600 F.,

or less, prior to their introduction into separating chamber I0. Chamber |0, as previously mentioned, is preferably operated at a substantially lower pressure than that employed at the outlet of coil 6 and the reduced pressure may range, for example,.from 150 pounds, or thereabouts, per square inch, superatmospheric, down to substantially atmospheric pressure, a superatmospheric pressure of the order of 60 to.100 pounds, or more, per square inch being preferred in this zone in order to permit the use of a substantial superatmospheric pressure in receiver 81. Fractionator I5 and the succeeding condensing and collecting equipment are preferably operated at substantially the same pressure as that employed in chamber I0, except for the normal pressure drop through these zones.

Stabilizer 53, when employed, may be operated to substantially strip the distillate supplied thereto of dissolved gases or operated to produce a stabilized distillate having a vapor pressure meeting requirements for commercial gasoline. These requirements range, at present, from 8 to l2 pounds per square inch, as determined by the Reid method. Obviously, the conditions 'employed in stabilize:I 53 may be varied considerably, depending upon the desired vapor pressure of the stabilized product. Normally, however, the .pressure employed in this zone may range from to 300 pounds, or thereabouts, per square inch, superatmospheric, with a top temperature of from to 125 F. and a bottom temperature of from 340 to 410 F. Ordinarily, condenser 61 and receiver 10 will be operated at substantially the same pressure as that employed in stabilizery 53, although lower pressure may be employed therein,when desired.

Preferably, absorber `43 is operated at a substantial superatmospheric pressure ranging from 60 to 150 pounds, or more, per square inch, which is ordinarily the same as that employed in receiver 31, although any desired lower pressure down to substantially atmospheric may be employed in the absorber, when desired.

As an example of one specific operation of the process, as conducted in an apparatus such as illustrated and above described, the charging stock is a straight-run Pennsylvania naphtha cooled to a temperature of approximately 650'F.,

partly by pressure reduction and partly by the introduction of stripped4 absorber oil into the transfer line between coil 6 and chamber Il. The separating chamber is operated at a superatmosphericv pressure of Aapproximately A pounds per square inch and this pressure is substantially equalized in the succeeding fractionating, condensing and collecting equipment. Fractlonator I5 is operated to form light and heavy reux condensates, the former being returned in regulated quantities, after cooling,l to the upper portion of chamber |0, while the light reflux condensate, after reboiling and substantial stripping, a predominant portion of which has a boiling range of approximately 300 to 570 F.-is, in part, cooled and utilized as absorber oil and, in part, returned to coil 6 i'or further cracking. The gas-containing distillate collected in receiver 31 has an end-boiling point of approximately 400 F. and is stabilized to aReid vapor pressure oi' approximately 8 pounds per square inch. The gases liberated in this product by stabilization are substantially condensed, the resulting normally gaseous condensate being recovered as polymerization stock, while the uncondensed gases from receiver 10 and from receiver 31 are supplied to absorber 43. Only light reux condensate' is utilized as absorber oil in this particular operation and the enriched absorber oil is substantially stripped of dissolved gases. The latter are supplied to condenser 34. The stripped absorber oil is returned in regulated quantities to line 8 as a cooling medium for the hot conversion products. The above described operation will yield per barrel of naphtha charging stock approximately 83% of stabilized gasoline of approximately 400 F. end-boiling point, an 8 pound Reid vapor pressure and with an octane number of approximately rI0, as determined by the motor method. The additional products of the process are about 4.8% of residual liquid and about 10 gals. of liquid polymerization stock per barrel of naphtha charged to the cracking operation. The polymerization stock contains approximately 32 mol. percent of readily polymerizable olefins consisting of propene and iso and normal butenes. The remainder of the polymerization stock consists essentially of propane and butane and a relatively small percentage of lighter normally gaseous fractions. In addition about 210 cubic feet of light unabsorbed gases are recovered per barrel charging stock. l

I claim:

l. A process which comprises subjecting hydrocarbon oil to cracking conditions of temperature and pressure in a conversion zone, removing the resultant heated conversion products from said zone and separating therefrom a relatively heavy reilux condensate, a lighter reiiux condensate, a final distillate, and gases, scrubbing at least a portion of said gases with a portion of said lighter reflux condensate to absorb heavier components of the former in the latter, stripping the resultant enriched reux condensate of the absorbed gaseous components and recovering the latter, and thereafter commingling at least a portion of and non-vaporous residue, fractionating the vapors to form a relatively heavy reux condensate and a lighter reflux condensate, substantially condensing the fractionated vapors, which consist essentially of materials boiling within the range of gasoline and gases, to form a gas-containing distillate, separating the latter from the remaining uncondensed and undissolved gases, separately stabilizing the gas-containing distillate to reduce its vapor pressure to the desired degree by liberating regulated quantities of dissolved gases therefrom, recovering the stabilized distillate, stripping a regulated quantity of said lighter reflux condensate of dissolved gases and cooling and contacting with said uncondensed and undissolved gases, whereby to absorb desirable high-boiling components of the gases, substantially stripping the resulting enriched absorber oil of absorbed gases, recovering desirable high-boiling normally gaseous materials liberated from the distillate by said stabilization and liberated from the enriched absorber oil by said stripping and directly commingling regulated quantities of the substantially stripped absorber oil with said hot conversion products, whereby to eect at least a portion of said cooling of the latter.

4. A -process such as dened in claim 3, wherein-the gases evolved from said distillate by said stabilization are supplied to the absorption step.

5. A process such as deiined in claim 3, wherea in the gases liberated from the enriched abthe stripped reflux condensate with heated conversion products discharged from said zone to cool such products.

2. The process as dened in claim 1 further characterized in that the gases supplied to the scrubbing step are separated from the 'final distillate by stabilization of the latter.

3. A process of pyrolytic conversion which comprises, heating a hydrocarbon oil to an active cracking temperature at substantial superatmospheric pressure, cooling the resulting hot conversion products suiciently to prevent deleterious further conversion thereof, separating the resulting cooled conversion products into vapors sorber oil by said stripping are cooled and returned to the zone wherein said gas-containing distillate is separated from uncondensed and undissolved gases.

6. A process such as dened in claim 3, wherein the gases liberated from the distillate by said stabilization and the gases liberated from the enriched absorber oil by said stripping are substantially condensed to form a normally gaseous condensate, which is recovered.

7. A process such as defined in claim 3, wherein the gases liberated from the distillate by said stabilization and the gases liberated from the enriched absorber oil by said stripping are substantially condensed to form a normally gaseous condensate, which is recovered, and wherein gases remaining uncondensed in the last mentioned condensation step are supplied to said absorption step.

8.A A process such as dened in claim 3, wherein said lighter reflux condensate employed as absorber oil includes high-boiling gasoline fractions.

CHARLES H. ANGELI. 

